Abstract

Excellent resistive switching memory characteristics were demonstrated for an Al/Cu/Ti/TaOx/W structure with a Ti nanolayer at the Cu/TaOx interface under low voltage operation of ± 1.5 V and a range of current compliances
(CCs) from 0.1 to 500 μA. Oxygen accumulation at the Ti nanolayer and formation of
a defective high-κ TaOx film were confirmed by high-resolution transmission electron microscopy, energy dispersive
X-ray spectroscopy, and X-ray photo-electron spectroscopy. The resistive switching
memory characteristics of the Al/Cu/Ti/TaOx/W structure, such as HRS/LRS (approximately 104), stable switching cycle stability (>106) and multi-level operation, were improved compared with those of Al/Cu/TaOx/W devices. These results were attributed to the control of Cu migration/dissolution
by the insertion of a Ti nanolayer at the Cu/TaOx interface. In contrast, CuOx formation at the Cu/TaOx interface was observed in an Al/Cu/TaOx/W structure, which hindered dissolution of the Cu filament and resulted in a small
resistance ratio of approximately 10 at a CC of 500 μA. A high charge-trapping density
of 6.9 × 1016 /cm2 was observed in the Al/Cu/Ti/TaOx/W structure from capacitance-voltage hysteresis characteristics, indicating the migration
of Cu ions through defect sites. The switching mechanism was successfully explained
for structures with and without the Ti nanolayer. By using a new approach, the nanoscale
diameter of Cu filament decreased from 10.4 to 0.17 nm as the CC decreased from 500
to 0.1 μA, resulting in a large memory size of 7.6 T to 28 Pbit/sq in. Extrapolated
10-year data retention of the Ti nanolayer device was also obtained. The findings
of this study will not only improve resistive switching memory performance but also
aid future design of nanoscale nonvolatile memory.